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**Definition of a chip set:
In short it is a set of  chips that allow a system designer to build a
computer.  If we restrict the term  'chip' to that of a microchip then
technically any microcomputer  contains a chip set, even  one based of
7400-series logic alone.

In the context of this document, a chip set is defined as any group of
chips used to implement  an IBM or IBM-compatible PC/XT/AT/386/486/etc
system.

There are 2 main categories that these chips fall into:
1. Direct copies or re-implementations of Intel chips
2. Chip sets sold as a set of chips to implement an IBM-compatible 
   that differ in some way to those used in an IBM system, e.g. not 
   pin compatible.

An  example of  the former  would be  some early  chips built  by VLSI
Technology (at the time known as VTI, to implement a 286:
o  VL82C37A is a: 82C37A DMA controller
o  VL82C59A is a: 82C59A interrupt controller
o  VL82C54A is a: 82C54 timer
o  VL82C612 is a: 74LS612 memory mapper
o  VL82C84A is a: 82284 clock generator and ready interface
o  VL82C88  is a: 82288 bus controller

These are  all direct replacements  for the parts  used in an  IBM AT.
Many companies had compatible versions of these chips.

An early example of the latter is the Chips & Technology NEAT chip set:
o  82C211 CPU/Bus controller, 
o  82C212 Page/Interleave and EMS Memory controller, 
o  82C215 Data/Address buffer 
o  82C206 Integrated Peripherals Controller (IPC).

The description does not map directly to the parts used in the IBM AT.
Later chip sets are often even more integrated sometimes consisting of
just one chip, although two seems to be the most common.

The latter  is generally considered  the definition of a  chip set, and
the former is not generally  considered a chip set per-se. However when
looking  at   the  early  chip sets   this  distinction  can   be  very
slight. Because of this,  sets of chips  meeting the criteria  for (1.)
have been included where possible. 

**'chip set', 'chip-set' or 'chipset'?...
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**Info needed on:...
**A note on VESA support of 486 chipsets....
**Datasheets:...
*_IBM...
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*AMD . . . . . . . [no datasheets, some info]...
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*Contaq  . . . . . [no datasheets, some info]...
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**82395SX     Smart Cache                                     12/17/90
***Notes:...
**82396SX     Smart Cache                                     12/17/90...
**82485       Turbo Cache (and 485Turbocache)                      c90...
**82489DX       Advanced Programmable Interrupt Controller    10/12/92...
**82495DX/490DX DX CPU-Cache Chip Set                           <Sep91...
**82495XP/490XP Cache Controller / Cache RAM (for i860)       06/05/91...
**82496/491     Cache Controller / Cache RAM (for P5 Pentium) 03/22/93...
**82497/492   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**82498/493   Cache Controller / Cache RAM (for P54 Pentium)    <Nov94...
**
**Later chipsets (basic spec):
**440 series:...
**450NX  (?)            06/29/98:...
**?????  (Profusion)    c:99...
**800 series...
*Headland/G2...
**HT44          Secondary Cache                                c:Jun92
***Info:
The  HT44 is  a  look-aside write-through,  80486SX,  486DX or  486DX2
secondary cache  controller. It is  packaged in an  inexpensive 84-pin
plastic-leaded chip carrier (PLCC).

Architecture
With  its look-aside architecture,  the HT44  fits beside  the CPU-to-
Memory bus  and not in  the data path.   Therefore, once the  HT44 has
been designed  into a  486 system, it  can be populated  for secondary
cache systems or left vacant for non-secondary cache systems. The HT44
is direct-mapped to the available address space.

Performance
The  HT44  has a  number  of  performance  enhancing features.   These
include zero-waitstate burst line fills  to the 486 on secondary cache
hits, and simultaneous 486 and secondary cache updates on read misses.

Memory Configurations
The HT44 supports  cache sizes from 32KBytes to  1MB. Both synchronous
and asynchronous  SRAMs are supported.  25ns SRAMs are  sufficient for
zero-wait-state operation at 33MHz.

Chip Set Support
The HT44 can,  be implemented with minimal glue logic  in a 486 system
with the  HTK340 (code  name Shasta) chip  set.  The registers  in the
HTK340  allow  for programming  of  non-cacheable and  write-protected
areas of  memory. The  HTK340 will support  the HT44  with synchronous
SRAMs only.   Future Headland chip sets will  support both synchronous
and asynchronous SRAM designs.

The HT44  can also be used  with some third-party  chip sets, however,
additional glue logic may be required.

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